1. Field of the Invention
The present invention relates to a system for production of high-purity hydrogen, a process for production of high-purity hydrogen, and a fuel cell system. More particularly, the present invention relates to a system for efficient production of high-purity hydrogen, a process for efficient production of high-purity hydrogen, and a fuel cell system provided with said system.
2. Description of the Prior Art
A process for hydrogen production is known which utilizes the steam reforming of a hydrocarbon and/or an oxygen atom-containing hydrocarbon, for example, methane, propane, methanol, ethanol or petroleum. The steam reforming is represented by the following formula in the case of, for example, reforming of methanol. EQU CH.sub.3 OH+H.sub.2 O.fwdarw.CO.sub.2 +3H.sub.2 ( 1)
Japanese Patent Application Kokai (Laid-Open) No. 295402/1988 discloses a process for producing hydrogen by conducting the reforming of formula (1) and recovering the formed hydrogen by the use of a hydrogen-separating membrane.
Since the reforming of formula (1) is an endothermic reaction, heat must be supplied from outside in order to allow the reaction to proceed or continue. In Japanese Patent Application Kokai (Laid-Open) No. 147902/1993, this heat is supplied by burning the portion of the reformed gas not permeable into the hydrogen-separating membrane (said portion still contains hydrogen and is hereinafter referred to as non-permeable gas).
A fuel cell is known as a means for utilizing the energy generated by the reaction of hydrogen and oxygen, as electric energy. For the efficient operation of a fuel cell, use of high-purity hydrogen is necessary. In the case of a solid polymer type fuel cell, in particular, it is necessary to reduce the CO concentration in reformed gas to several ppm or less in order to prevent platinum (an electrode catalyst) from being poisoned by CO. Hence, it has been studied to combine an apparatus allowing for hydrogen production such as mentioned above, with a fuel cell to use the combination as a portable power source or in an electric automobile.
Studies made by the present inventors indicated that the invention as described in Japanese Patent Application Kokai (Laid-Open) No. 147902/1993 has the following problems.
As shown in the formula (1), 3 moles of hydrogen are obtained from 1 mole of methanol. If the hydrogen recovery by the hydrogen-separating membrane, i.e. the proportion of the hydrogen passing through the membrane to the total hydrogen formed is 100%, the non-permeable gas is zero, and there is supplied no heat necessary for proceeding and containing with methanol reforming. Hence, the hydrogen recovery must be reduced to 70-80% to secure the heat required for the reforming. With this reduction in hydrogen recovery, the amount of hydrogen formed from 1 mole of methanol decreases to about 2 moles, reducing the efficiency of hydrogen production.
Further, in the heat supply by combustion of non-permeable gas (containing hydrogen), which is external heating, the efficiency of heat conduction is low.
Furthermore, in the process disclosed in Japanese Patent Application Kokai (Laid-Open) No. 147902/1993, which burns part of the hydrogen formed by reforming, to use the generated energy as a heat source for reforming, the efficiency of hydrogen production is not satisfactory. Accordingly, in applying the process to an electric automobile provided with a hydrogen-producing apparatus and a fuel cell, the fuel utilization is low.
Object and Summary of the Invention
In view of the above situation, objects of the present invention are to provide a system for production of high-purity hydrogen, superior in efficiencies of hydrogen production and heat conduction and low in cost of hydrogen production; and a process for production of high-purity hydrogen using said system.
Another object of the present invention is to provide a fuel cell system utilizing the above system for production of high-purity hydrogen.
In order to achieve the above objects, the present inventors made a study and determined that the above objects can be achieved by utilizing the partial oxidation (an exothermic reaction) of a hydrocarbon and/or an oxygen atom-containing hydrocarbon (e.g. methanol), represented by the following typical formula: EQU CH.sub.3 OH+(1/2)O.sub.2 .fwdarw.CO.sub.2 +2H.sub.2 ( 2)
The finding has led to the completion of the present invention.
According to the present invention there is provided a system for producing high-purity hydrogen by reforming a hydrocarbon and/or an oxygen atom-containing hydrocarbon to form a reformed gas containing hydrogen and separating the reforming and partial oxidation and a hydrogen-separating membrane, the reforming chamber being thermally connected with the vaporization chamber.
The present invention further provides a process for producing high-purity hydrogen by reforming a hydrocarbon and/or an oxygen atom-containing hydrocarbon to form a reformed gas containing hydrogen and passing the reformed gas through a hydrogen-separating membrane to selectively recover and oxygen or air to give rise to steam reforming and partial oxidation therein.
The present invention furthermore provides a process for producing high-purity hydrogen by reforming a hydrocarbon and/or an oxygen atom-containing hydrocarbon to form a reformed gas containing hydrogen and passing the reformed gas through a hydrogen-separating membrane to selectively recover and oxygen or air to give rise to steam reforming and partial not permeable into the hydrogen-separating membrane and the heat generated by the partial oxidation are utilized for the heating and reforming of the hydrocarbon, water and oxygen or air.